The proposed research seeks to understand how ecological conditions of animals influence the evolution of their mechanisms of communication, and how the physiological properties of sensory receptors evolve to enhance communication signal perception in various environments. Using electrical communication as a model system, the research uses two main approaches: (1) field studies of electrical communication and its role in the social behavior of Mormyrid electric fishes from Africa, and (2) electrophysiological studies of stimulus filtering by electroreceptors in mormyrids and also in South American gymnotid electric fishes. Field work, to be conducted near the Ivindo River in Gabon, West Africa, will concentrate on the mechanisms of species recognition and other types of signaler identification; on social signaling; on the properties of signal transmission in natural environments; and on the ecology of mormyrids. Electrophysiological studies of electroreceptors will use a comparative approach, and will examine the filtering characteristics of electroreceptors of several species of gymnotid fishes which differ markedly in the frequency of the discharge of their electric organs, and several species of mormyrids that differ markedly in the waveform of their electric discharges. Central control of tuning specificity will also be examined and a preliminary study of the plasticity of stimulus filtering will be undertaken. Bibliographic references: Griffin, Donald R. and C.D. Hopkins, 1974. Sounds audible to migrating birds. Anim. Behav., 22:672-678. Hopkins, Carl D. 1974. Electric communication: functions in the social behavior of Eigenmannia virescens. Behaviour, L3-4:270-305.